1. Field of the Invention
This invention relates to and has among its objects the provision of novel organic compounds and the use thereof in insect control, particularly as anti-procreants. Further objects of the invention will be evident from the following description wherein parts and percentages are by weight unless otherwise specified. The symbol .phi. is used herein to represent the ##STR1##
2. Description of the Prior Art
Currently, there are various means for controlling insect populations. For example, one may apply an insecticide to insects or to their habitat. This method of control, however, has the disadvantage that the insecticide may cause harm to humans, animals, and useful insects (bees, for instance). Biological control of insects may be attained by employing compounds which serve as anti-procreants, i.e., chemosterilants or oviposition inhibitors. In the first type of biological control, a chemical (called a chemosterilant) is administered to the insects, which then become sexually sterile. The sexually sterilized insects mate with fertile insects, but the eggs laid do not yield any progeny. The result is a decrease in population of the insects. Another method of biological control involves administering a chemical (oviposition inhibitor) to the insects, with the result that the female species do not posit (lay) any eggs. Consequently, no progeny are produced and a decrease in insect population is thus attained. Although the above means of biological control encompass two distinct ideas, the chemical compounds which produce the above effects may be termed generally as anti-procreants, that is, compounds which act either as chemosterilants and/or oviposition inhibitors and prevent procreation of the species.
The biological method of insect control offers many advantages over the usual method of applying an insecticide to insects or their habitat. For example, it avoids harm to humans, animals, and useful insects.
In controlling insects by sterilization or oviposition inhibition, a suitable compound is administered to a group of insects and these are then released in a locus where insects of the same species are present. As noted above, the treated insects mate with fertile ones but without producing progeny so that the overall population is decreased.
Insect anti-procreants are known and described in U.S. Pat. Nos. 3,959,489 ('489), 4,049,722 ('722), and 3,968,234 ('234). In '489 and '722 sexual sterility and oviposition in flies were inhibited by feeding the flies sufficient amounts of the following compounds: ##STR2## wherein n is 2 or 3.
Sexual sterility, but not oviposition inhibition, was obtained in '234 by employing compounds of the structure- ##STR3## wherein Alk is an alkyl radical containing 1 to 4 carbon atoms.
Another means for controlling insect populations involves the use of compounds which inhibit the growth of the insect larvae. Such compounds are often referred to in the art as juvenile hormone mimics. These agents do not kill the larvae, but rather prevent the growth thereof beyond the larval or pupal stage. Consequently, the number of adults is substantially reduced. The juvenile hormone mimics actually cause several different situations, all of which result in controlling insect population. First of all, most of the treated larvae do not reach adulthood. Thus, the larvae survive for a period of time (possibly an entire growing season) as either larvae or pupae, and then die. During that period the larvae are, of course, very susceptible to predation and injurious climatic conditions. Furthermore, they are themselves incapable of reproduction, thus reducing the insect population for the next growing season. Secondly, some of the treated larvae may develop to various stages of adulthood. For example, the adult insect may only partially eclose, i.e., emerge from the larval or pupal shell. On the other hand, full eclosion may occur but the adult insect is either malformed or dead. In either case, the population of adult insects is substantially reduced.
The growth-inhibiting compounds have many advantages over insecticides and the like. First, the growth-inhibitors do not yield unwanted ecological side effects. Secondly, since the growth inhibitors act as juvenile hormone mimics, the insects do not develop a tolerance to the compounds. Thus, the compounds will not eventually become ineffective. Third, the growth-inhibiting compounds are not harmful to beneficial insects or mammals because they are quite specific for a particular kind of insect.
Larval growth-inhibiting compounds have been disclosed. For example, in Chemical Abstracts, Volume 80, No. 768 h (1974), and Mosquito News, Volume 31, No. 4, pp. 513-516 (1971), certain polybutylbenzyl phenols are offered as insecticides to control mosquitos. Generally, these compounds have the structure- ##STR4## wherein R is independently hydrogen or methyl.
Finally, the following compound was described as a mosquito larvicidal agent in Chemical Abstracts, Volume 82, 125071 y (1975) and in German Offen. 2,425,713: ##STR5##
It should be noted that sexual sterility and oviposition inhibition, on the one hand, and larvicidal or juvenile hormone activity, on the other, although related generally because they are forms of insect population control, are different and unrelated concepts. In the former, insects exposed to the anti-procreant agents exhibit one or both of the following results: First, females may not posit any eggs. Second, even though eggs are posited, they do no hatch or otherwise further develop because the anti-procreant compound has induced sexual sterility in either the adult male or adult female or both. In any case, procreation is prevented.
Juvenile hormones are essential for growth and development of young larvae. The last instar larvae are equipped with internal physiological mechanisms which interrupt the secretion of these juvenile hormones. The result is that larval growth and development are replaced by pupal and adult growth-a process generally known as metamorphosis. The metamorphic process can be thwarted by supplying the larvae with juvenile hormone or a juvenile hormone analogue before a certain critical period is reached. If this is done, partial or complete inhibition of metamorphosis is realized and adults either do not form or are misformed.